1. Field of the Invention
The present invention relates to a method for cleaning a lead zirconate titanate (PZT) thin film using an etchant.
2. Description of the Related Art
A PZT thin film is a thin film having La, Sr, Ca, Sc, Nb, Ta, Ni, Fe or Er added to Pb(ZrxTi1xe2x88x92x)O3. In manufacturing a semiconductor device such as a ferroelectric random access memory (FRAM) using the PZT thin film, the PZT thin film is degraded by various processes. According to the growth mechanism of a thin film, defects or components impediment to ferroelectric characteristics are concentrated on the surface of the PZT thin film. These materials are generally called a secondary phase materials, e.g., PbO or pyrochlore phase materials, which are paraelectric materials without ferroelectricity to thus degrade capacitor characteristics. Since the pyrochlore phase is thermodynamically weaker than a perovskite phase, it is liable to be damaged during integration, thereby accelerating degradation of capacitor characteristics. Also, during dry etching, layers damaged due to plasma are produced at the lateral surfaces of the PZT thin film. These layers directly connect an upper electrode and a lower electrode, and analysis thereof proves that they do not have crystallinity and the thicknesses thereof are 100 xc3x85 or less (please see Scanning Electron Micrograph (SEM) picture.) Also, they function as a leakage path due to their strong metallic characteristic.
FIG. 1 is a cross-sectional view of a ferroelectric capacitor manufactured by a conventional method without a cleaning process. As shown in FIG. 1, the conventional ferroelectric capacitor is constructed such that a PZT thin film 2 is formed on a lower electrode 1 and an upper electrode 3 is deposited on the PZT thin film 2 to then be etched in a predetermined dimension. Here, in the case of dry-etching the PZT thin film 2, a thin etching damaged layer 4 due to plasma remains on lateral surfaces of the PZT thin film 2, which increases leakage current.
To solve the above problems, it is an objective of the present invention to provide a method for cleaning a PZT thin film, which improves ferroelectric capacitor characteristics by eliminating secondary phase crystals or etching damaged layers from the top surface or lateral surface of the PZT thin film generated during manufacturing of the same.
To achieve the first objective of the present invention, there is provided a method for cleaning a PZT thin film using an etchant comprising the step of submerging a PZT thin film in an etchant in combination of HF and acetic acid to etch the surface of the PZT thin film.
In the present invention, alcohol may be further added to the etchant in combination of HF and acetic acid. Preferably, the alcohol is at least one selected from the group consisting of methanol, ethanol and propanol. Instead of alcohol, a polar solvent which is at least one selected from the group consisting of DMSO, DMF, dioxane, THF, NMP, pyridine, CCl3H and CClH3 may be used.